With the rapid development of communication technology and the significant increase of terminals, technology of Multi-user Multiple-Input-Multiple-Output (MU-MIMO) has been widely applied. MU-MIMO is to improve average throughput of a system, and data of multiple downlink terminals is multiplexed on a same time and frequency resource to obtain Spatial Division Multiple Access (SDMA) gain. Since it is difficult for the terminals to realize detection unitedly, interference between the terminals becomes an important factor affecting the MU-MIMO performance. In order to conduct effective communicates with the terminals on a same time and frequency resource block, it is necessary to make MU-MIMO pilots independent or orthogonal from each other. A base station usually employs pre-coding technology to perform a pre-processing unitedly on data of the multiple terminals, to avoid the terminals to interfere with each other, and to facilitate the terminals to distinguish their signals accurately.
In the conventional technology, the pilot interference is reduced by a combination of a Scrambling identity (SCID) and a demodulation pilot port. Since a two-dimensional Walsh sequence (Walsh code) is used to distinguish, there are only two orthogonal demodulation pilot ports. In a case that the number of streams of MU-MIMO is greater than two, pseudo-orthogonal pilots occur due to the combination of SCID and the two-dimensional Walsh code.
In a case that a four-dimensional Walsh code is used to distinguish, four orthogonal demodulation pilot ports are obtained, which can solve the problem of the pseudo-orthogonal pilot in theory. Although the current Long Term Evolution (LTE) R10 protocol supports the four-dimensional Walsh code, MU-MIMO employs an agreement of the LTE R9 protocol which specifies that two streams of MU-MIMO employ the two-dimensional Walsh code to guarantee the orthogonality of the pilots and more than two streams of MU-MIMO employ a combination of the two-dimensional Walsh code and SCID to reduce pilot interference. However, in a case that the number of streams of MU-MIMO is greater than two, pseudo-orthogonal pilots occur due to the combination of SCID and the two-dimensional Walsh code.
In addition, the terminal cannot recognize the four-dimensional Walsh code for transparent MU-MIMO.